Although never read that, easy answer: Because they thought they would get air support, rather than allowed to die.
Knowing this attack went on for some 8 hours, and reading about the military assets in the area, I've come to the conclusion that the WH or some political flag officer told those assets to stand down. IIRC, some admiral or general was fired because he told the WH he will respond. Am I off mark?
Hamm?
No.
Someone on the ground communicated with something in the air. Otherwise you wouldn't give away your position painting a target.
It stinks, doesn't it?
5.56mm